Telling the Stories of the Unidentified

According to the National Missing and Unidentified Persons System (NamUs), 600,000 individuals go missing in the United States each year. While many are quickly found, it is estimated that 4,400 unidentified bodies are recovered each year, with 1,000 of them remaining unidentified after one year. All told, there are currently more than 40,000 sets of human remains listed as unidentified in the United States.


Written by: Tara Luther, Promega



While advances in DNA technology have assisted in providing identities for many, limitations remain, especially with populations that are non-native to the United States. Many who have perished while attempting to migrate from Latin American countries have no genetic relatives in the United States, and they are undocumented. Those who may be relatives are hesitant to come forward to submit DNA, because they are also undocumented. Without reference samples to use for comparison, the power of DNA is limited.


Additionally, many of the remains found have been exposed to the elements for years. Often, little or no tissue exists, and the skeletons may be incomplete, which makes obtaining a DNA profile challenging.


In cases where medical examiners are limited by the information that DNA analysis can provide, forensic anthropologists may be able to shed some light. As specialists in the hard tissues of the body, such as teeth, bones, fingernails, and even hair, forensic anthropologists tell the story of the deceased by providing a biological profile. This profile includes the sex, age, ancestry, living stature at the time of death, and a rough post-mortem interval. They are also able to determine if trauma or disease was present.


Once a biological profile has been completed, specially trained forensic anthropologists are able to perform an isotopic analysis to help determine where a person may have lived.


Isotopes vary depending on geographical location and may provide clues as to where a person was born, where they have recently lived, and where they were just months ago. When dealing with cold cases, this information can provide investigators with a place to start.


Traditionally, five different isotopes are used for forensic analysis. Hydrogen and Oxygen isotopes point to drinking water consumed. Carbon and Nitrogen isotopes provide information on a person’s diet. Finally, Strontium, which is found in both food and water, can suggest additional information about diet or local environments, depending on the tissues tested.


There are three main tissues tested, and each sheds light on a different stage of a person’s life. Teeth, such as the first molar, begin to form in utero and complete themselves by the time a person turns three. Performing an isotopic analysis on the oxygen levels within a tooth sheds light on where a person was born. Longer bones, like the femur, provide information on the past 20 years of a person’s life, while spongy bones like a rib or the cranium shed light on where someone has lived in the past five years. Finally, if you’d like to know where a person has been in the past several months, performing isotopic analysis on the oxygen levels of the hair or fingernails will be a great indicator.


Deceased, undocumented border-crossers from Latin America pose additional challenges when performing Oxygen and Hydrogen isotope analysis. The problem dates to the early 1900’s as Mexican states began to implement municipal water plans. Uneven development, poor water sanitation, damage from earthquakes, and deficiencies in repairs led to disparities in the ability to meet the need and water scarcity among Mexican states. Additionally, water-borne diseases such as cholera, amebiases, and cysticercosis, and over-chlorination have led to a loss of confidence in the municipal water. As a result, between 80-100% of Mexicans report using bottled water as their only source of drinking water, especially those under 40 years of age.


This means that the bottled water consumed could originate from an entirely different state than where the drinker is living, which can lead to discrepancies in the isotopic analysis. To counteract this, researchers have begun to collect samples from available bottled water.


Currently, researchers are working to develop mathematical modeling that would allow forensic anthropologists to predict isotope levels and a region of origin for a victim based on what is already known about a region, such as precipitation. Doing so may one day allow for the prediction of a migrational pathway based on different tissue samples available from a victim. Dialing in the modeling may one day allow investigators to determine the path an individual had taken, which could prove to be powerful in the fight against human trafficking and illegal immigration.